Ocean electric field measurement can be applied to the exploration of marine geological structures, exploration of marine mineral resources, monitoring of marine organisms, and discovery and tracking of moving targets in and at sea. Due to the complexity of the marine environment and the working mechanism of the modulated ocean electric field sensor, the sensing output contains complex noise components. Only by suppressing these noises and obtaining a high signal-to-noise ratio, reliable electric field signals can be extracted from the sensing output. A single noise suppression method is difficult to effectively reduce multiple types of noise. Therefore, this article proposes a composite denoising method targeting the noise characteristics in the output signal of modulated ocean electric field sensors. The noise is divided into three categories, including broadband random noise, noise within the useful signal frequency band, and noise outside the useful signal frequency band. Utilize the uncorrelation between broadband random noise and useful signals, and use adaptive filters to suppress broadband random noise. A bandpass filter is adopted to suppress noise outside the useful signal frequency band. Finally, the useful signal is extracted from the sensing output through variational mode decomposition, and demodulation is achieved through envelope detection. Compared with using bandpass filtering denoising, empirical mode decomposition denoising, and wavelet denoising alone, the sensor output signal-to-noise ratio processed by the proposed method is improved by more than 12 dB, ensuring reliable demodulation of modulated ocean electric field sensing signals.